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Solution runs, but obtain huge (1e+12) displacements

I have set up a case which completes in optistruct however produces unrealistic displacements in the order of e+12. I believe the part is fully constrained with two 6DOF constraints at the top and bottom, with only 2 forces added for braking torque and braking force + Weight. Could anybody advise what I should try next?

Thanks,

Anthony

Iteration Subcase Variable Grid/Elem ID Value
---------------------------------------------------------------------------------------------------------
0 1 MaxDisp 27810 -0.203066E+12
0 1 MaxStress 354993 34.7560
0 0 Objective_MinimizeMASS 0 0.541146E-03
0 0 MaximumConstraintViol% 0 0.00000

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Altair Forum User

Hi,

There are 5K+ free nodes in your model.

Use Equivalence panel (Shift+F3) to connect these nodes to the nearest node(s).

ajd-brown

Hi Prakash,

Just to ensure I understand the problem:

You say there are 5000 free nodes, presumably, these are the nodes where my Design and NonDesign spaces meet but are not joined together properly?

So my using the equivalence tool it found ~2400 Nodes which were close to but not equal. So by making these nodes equivalent, they are then connected to the rest of the model rather than floating in space (which is why they got infinite displacement?) and the displacement should return to normal?

You say there were 5000+ free, the equiv tool found ~2400, is this ~2400 pairs of similar nodes (=~5000) or am I still missing something?

As you can see from the attached image, its iterating! Thank you so much for your help!

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Altair Forum User

they are then connected to the rest of the model rather than floating in space (which is why they got infinite displacement?) and the displacement should return to normal?

Yes,

You say there were 5000+ free, the equiv tool found ~2400, is this ~2400 pairs of similar nodes (=~5000) or am I still missing something?

The number of nodes depends on the tolerance value in the Equivalence panel. My value is very small and this could be the reason.

if the results are OK and makes sense then the model is fine.

ajd-brown

Hi Prakash,

The results are similar to what I would expect from the loads however the stress constraint in the topology design variable is being violated / completely ignored!

I gave a value of 125 in the DESVAR parameters, but the solver screen shows a stress of ~350, even after 50 iterations!

Why is my 125 not being taken into account / What can I do to perform a stress constrained topology optimization?

Regards,

Anthony

Rahul Rajan_21763

We have limitation for stress constrained topology optimization.Online user guide for optistruct conatins more info on this topic.Coming version have some feature on stress constraint.Soon we are expecting version HW 14.0 to get release.we will update you once we get official release.

Regards

Rahul R

ajd-brown

Hi Rahul,

Ok thank you for the info, can size optimization be used simultaneously or after with a stress constraint?

What is the best alternative if not?

Regards,

Anthony

Rahul Rajan_21763

I hope you would have aware of the attached info.This is what i mean in my above post.

See DTPL card commnent1 aswell.

Regards

Rahul R

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Altair Forum User

can size optimization be used simultaneously or after with a stress constraint?

Anthony,

I can see that your model has solid elements. So Size optimization is not the right choice. You can do a shape optimization.

ajd-brown

Hi Rahul,

I believe my model should be OK for topology with a single VM stress, I do not need to place different stress constraints in different parts of the model.

I am not familiar with the DSIZE card or its location in the software , how can I implement this in a topology optimization? I think I have already used the 'STRESS optional continuation line on the DTPL' as shown in the image below but this failed to constrain the optimization or am I mistaken?

Regards,

Anthony

----------

Prakash,

Thank you for your advice!

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Rahul Rajan_21763

Please try same with version 14.0.Attached is the screenshot for enhancement in stress response.

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